Mammary prostheses are used to enhance the appearance of human breasts, normally female breasts. The prostheses are used to add volume to a breast which may be required after removal of a tumour, or to enhance the aesthetic appeal of a breast.
A mammary prosthesis typically comprises a resilient plastics material bladder which is filled with a liquid. The bladder is normally manufactured from a silicone rubber filled with a gel, typically a silicone gel.
A problem with silicone gel is rupturing of the bladder which releases the gel in the patient's body. If a bladder ruptures in vitro the released gel cannot be recovered, or at least not all of it.
A serious complication of silicone gel filled bladder prostheses is capsular contraction, which is a condition in which tissue surrounding the prosthesis after it has been implanted into a patient hardens. This hardening of the tissue takes place in response to silicone gel which routinely leaks through the bladder. The leaking is an accepted side effect of these prostheses and capsulation is, in part, relied upon to contain silicone which leaks from the bladder.
One likely driving force for the bleed of the filler material, and specifically silicone gel, is Brownian motion, which is a result of thermal molecular motion of particles in a liquid environment. According to this phenomenon, there is random movement of the silicone gel particles inside the shell of the prosthesis. Since the atomic structure of solid silicone, from which the shell of the prosthesis is manufactured, is larger than the size of silicone gel molecules, some of the gel molecules will pass through the shell because of the Brownian motion. In essence, the shell is like a mesh through which the gel particles can be squeezed.
Another phenomenon which also likely acts as a driving force is osmotic pressure. According to Merriam-Webster's Collegiate Dictionary, osmosis is the “movement of a solvent through a semi-permeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.” In the case of a silicone gel filled mammary prosthesis, there is a higher concentration of gel inside the shell of the prosthesis than outside the shell. Body fluid, of which there is plenty in supply, will tend to move into the prosthesis because of osmotic pressure in an attempt to equalize the concentrations of silicone gel on opposite sides of the shell. This increases the fluid pressure inside the prosthesis which contributes as a driving force to push fluids out of the prosthesis, including silicone gel. At the same time the silicone gel, which is at a higher concentration inside the shell than in the human body and is at least to some degree a solute, experiences osmotic pressure to move from a higher concentration to a lower concentration through the shell, i.e. from the prosthesis into the body.
There have been attempts to limit the spread of the silicone by formulating it as a ‘sticky’ gel. The intention with this is to keep the silicone gel together and to ease surgical removal. However, this does not solve the problem since the sticky gel adheres to anything it touches including the patient's organs and the surgeon's gloves. Removing the sticky gel is not an easy matter and 100% removal of all leaked gel is generally not possible.
In some countries, the use of bladders filled with silicone gel has been banned due to the health risks associated with it. To overcome this problem prostheses have been developed which comprise a bladder filled with liquid other than silicone gel, for example saline solution. This solves the problem of the leaking which causes capsular contraction. If such a prosthesis ruptures the patient doesn't need surgery to remove the liquid, since saline is harmless to the human body.
A problem associated with saline filled prostheses is that these prostheses are generally inserted empty into a patient and filled in vitro by means of a filler tube and non return valve. These systems are often problematic and leakage of saline through the filler tube arrangement often occurs.
Another problem with saline filled prostheses is that the viscosity of saline is different from silicone gel, which causes these prostheses to have an unnatural feel once implanted.
Another problem with conventional prostheses is that details of implanted prostheses are not readily ascertainable from outside the body. In some instances it is necessary to determine details, such as size and type of implant or the date on which the prostheses was implanted on short notice and preferably without surgical procedure. Such instances may include a medical emergency such as may arise following an accident. It may also occur during routine procedures.
It often happens that people are unable to convey details of a prosthesis to medical personnel which may leave the medical personnel with no option but to determine details of the implanted prosthesis by means of expensive scanning equipment, for example MRI scanning, or surgery. Neither of these is desirable, the first due to the cost involved and second due to the invasive and drastic nature and the cost thereof.
A specific problem exists with female patients whom had received breast augmentation surgery and experience complications. In many instances, these patients are not able to recall the make of prosthesis they have received and in even more cases, not the size of prosthesis received. If an existing prosthesis needs to be replaced the surgeon needs to have all possible sizes available during surgery to fit the correct size prosthesis.
A further aspect of breast prostheses that is problematic relates to the manufacturing of the prostheses. In most cases a bladder is formed which include an opening at the operatively posterior side of the bladder. This opening is needed in the forming of the bladder to enable removal from the mould on which the bladder is formed. The opening is sealed by means of a disc which is placed inside the opening and adhered to the bladder by means of pressure. A problem with this type of seal is that it is not a seal that is formed by means of a bond between the two surfaces forming part of the seal, but rather an adhesion type seal of the disc against the bladder which, after the bladder has been filled, relies on pressure from the gel inside the bladder to maintain the seal. It is possible to disengage such a seal by exerting on the disc from the outside.
The above mentioned problems have been exemplified by way of a mammary prosthesis, but similar problems exist with other types of prostheses. Examples of these include prostheses which are used to enhance the appearance of buttocks, cheeks, and biceps. The concerns about the safety of silicone gel filled prostheses are equally applicable to these procedures, as are problems which exist with saline filled prostheses.